Genetically modified (GM) pigs hold great promises for pig genetic improvement, human health and life science. When GM pigs are produced, selectable marker genes (SMGs) are usually introduced into their genomes for host cell or animal recognition. However, the SMGs that remain in GM pigs might have multiple side effects. To avoid the possible side effects caused by the SMGs, they should be removed from the genome of GM pigs before their commercialization. The Cre recombinase is commonly used to delete the LoxP sites-flanked SMGs from the genome of GM animals. Although SMG-free GM pigs have been generated by Cre-mediated recombination, more efficient and cost-effective approaches are essential for the commercialization of SMG-free GM pigs. In this article we describe the production of a recombinant Cre protein containing a cell-penetrating and a nuclear localization signal peptide in one construct. This engineered Cre enzyme can efficiently excise the LoxP-flanked SMGs in cultured fibroblasts isolated from a transgenic pig, which then can be used as nuclear donor cells to generate live SMG-free GM pigs harboring a desired transgene by somatic cell nuclear transfer. This study describes an efficient and far-less costly method for production of SMG-free GM pigs.
Four different ratios of river sand, ceramic pellets, vermiculite and perlite (1:1), and field soil were selected as the
substrates in this experiment, and four gradient levels of root waterlogging, half waterlogging, full waterlogging
and normal were set to investigate the effects of different gradients of waterlogging stress on the root morphology
of Taxus chinensis var. mairei seedlings under different substrates. In this study, the root anatomical structure of
Taxus chinensis var. mairei under different waterlogging stress was observed by the paraffin section method. The
roots of T. chinensis var. mairei were diarch, with no pith and resin canals. There was a large number of tannins in
the pericycle of the aerial adventitious roots of seedlings adapted to waterlogging. Also, the endodermis has
obvious casparian strip thickening, and there were 4-5 layers of large parenchymatous cells in the close to the
inner side of the pericycle in the vascular cylinder, which could increase the storage capacity, and transport capacity of the root. Under the treatment of root waterlogging stress, the development of plant roots in the mixed
substrate of vermiculite and, perlite was the earliest. Under half waterlogging stress, T. chinensis var. mairei seedlings treated with various substrates all could better adapt to the environment of waterlogging stress. Under the
stress of fully waterlogging, the roots of seedlings planted in river sand substrate developed secondary growth. 相似文献